Second to fourth stage graphite intercalation compounds (G.I.C.) with 70% perchloric acid have been synthetized according to a purely thermal process, and characterized by chemical analysis and 001 X-ray diffraction. Moreover, an exothermic transformation, evidenced by means of thermal analysis of these compounds, was assigned to the intercalate dissociation during the sample exfoliation. This specific property was utilized to carry out the exfoliation of natural and artificial graphites with particles of different diameters. Exfoliated materials were characterized by scanning electron microscopy (S.E.M.). The specific surface area and surface homogeneity of the samples were determined by means of krypton adsorption.